1. Field of the Invention
The present invention relates to wheelchairs and, more particularly, to wheelchairs provided with anti-tipping devices for preventing the wheelchairs from tipping over rearwardly.
2. Description of the Related Art
A conventional wheelchair comprises a seat on a frame, a pair of side wheels supporting the frame and, forwardly from the side wheels, a pair of front castors.
Various anti-tipping devices have, in the past, been proposed for counteracting the problem that, when the chair is required to move forwardly over an obstruction, for example over a curb of a sidewalk, the front castors must be raised by a certain amount, which inevitably tilts the wheelchair backward by a corresponding amount, and there is therefore a risk that the rearward tilting of the wheelchair and its occupant may cause their joint centre of gravity to be displaced rearwardly to such an extent that the wheelchair and its occupant fall backwardly.
For example, in U.S. Pat. No. 3,848,883, issued Nov. 19, 1974, to Stephen J. Breacain, there is disclosed an anti-tip apparatus for a wheelchair which includes a main tube extending laterally and rearwardly from the rear frame upright of a wheelchair, with extension tubes slidably received in the main tubes and spring-biased to a retracted position. The extended ends of the extension tubes are joined by a transverse support tube, and a wheel or coaster is provided at the end of each extension tube. A manually releasible spring detent latch on each main tube holds the apparatus in the extended position, allowing the wheelchair occupant safely to tip the chair back onto the extended wheel or coaster to negotiate steps and curbs and to retract the apparatus when maneuvering in close quarters. However, the latch is located behind the wheelchair seat, in a position in which the latch is not accessible to the occupant of the seat. There is no mechanism which can be operated by the occupant, while seated in the seat, for extending and retracting the wheel or coaster.
U.S. Pat. No. 3,580,591, issued May 25, 1971, to H. Franklin Coffey et al., shows another type of wheelchair anti-tipping device which, again, is located behind the wheelchair seat in a position inaccessible by the occupant of the seat and which also has no mechanism for extending and retracting the anti-tipping device.
U.S. Pat. No. 3,573,877, issued Apr. 6, 1971, to Burton H. Locke, teaches a wheelchair with a curb-climbing structure comprising a lifting means to be actuated by the occupant of the chair to raise the rear of the chair to a curb level after the front portion of the chair is placed on the curb.
It is, however, an object of the present invention to provide an anti-tipping device intended for use in circumstances other than when the chair is moved over an obstruction, e.g. for use when the chair is negotiating a hill or is being used in a sport, the anti-tipping device being retractable when the chair is moved over a curb or other obstruction.